What color is it?: As you can see above and below, this is
a true synthetic opal with colors that closely emulate natural
opal.

What is the story behind this
gemstone?: This is a Gilson
Synthetic Opal. The process used is just like a natural opal,
with silicon spheres being generated that line up like soldiers
in a straight line formation. Just like the natural counterpart,
this has the effect of producing a diffraction grating of light
into the spectral colors or refraction. The spheres are then surrounded
by a material that is strong enough to withstand cutting and polishing
to form this synthetic opal. It should be noted that materials
other than silicon can be used to make these gem materials, but
only silicon based material can properly be called synthetic opal.

Here's the rest of the story on
this synthetic opal......

Chemical: Si02 (silicon....glass)

Formation: According to Webster in Gems (Butterworth-Heinemann,
1997) the formation is by dispersing an organic silicon compound
in an alcohol-water mixture. When ammonia or similar mild alkali
is added to the mixture, silica spheres occur, which are then
allowed to settle into the above referenced rows creating the
diffraction grating effect of opal.

Crystal System: Amorphous

Unusual Properties: Lizard skin effect

RI: 1.450 + -

Optical Character: none

Hardness: 6 + -

Specific Gravity: Average 2.15

Special Identification Properties: As shown above and below,
the Gilson Opal has a diagnostic lizard skin effect
as seen in the photographs. This is easily seen in a 10x loupe,
and is diagnostic for a Gilson Synthetic Opal.